Source holder collimator for encapsulating radioactive material and collimating the emanations from the material

ABSTRACT

This invention provides a transportable device capable of detecting normal levels of a trace element, such as lead in a doughnut-shaped blood sample by X-ray fluorescense with a minimum of sample preparation in a relatively short analyzing time. In one embodiment, the blood is molded into a doughnut-shaped sample around an annular array of low energy radioactive material that is at the center of the doughnut-shaped sample but encapsulated in a collimator, the latter shielding a detector that is close to the sample and facing the same so that the detector receives secondary emissions from the sample while the collimator collimates the primary emissions from the radioactive material to direct these emissions toward the sample around 360* and away from the detector.

United States Patent 91 Laurer [450] Jan. 22, 1974 Primary Examiner-James W. Lawrence Assistant ExaminerC. E. Church Attorm: Agent. or FirmJohn A. Horzm [75] Inventor: Gerard R. Laurer, Monroe, NY. [57] ABSTRACT r [73] Assignee: The United States Of mer 85 This invention provides a transportable device capable represented by the United Stat of detecting normal levels of a trace element,- such as Atomic Energy Cmmnission, lead in a doughnut-shaped blood sample by X-ray Washington, DC fluorescense with a minimum of sample preparation in 22 d: 31 1973 a relatively short analyzing time. In one embodiment, 1 1e Jan the blood is molded into a doughnut-shaped sample PP 328,154 around an annular array of low energy radioactive material that is at the center of the doughnut-shaped 52 US. Cl. 250/272 250/273 Sample but encapsulated in a Qnimamr, the lane 51 Im. Cl. Gtilr 23/22 shielding detect that is the Sample and [58] Field of 250/272 273 274 facing the same so that the detector receives secondary emissions from the sample while the collimator [56] Reerences Cited collimates the primary emissions from the radioactive material to direct these emissions toward the sample UNITED STATES PATENTS around 360 and away from the detector.- 3,011,060 ll/l96l Dorenb'osch 250/272 10 Claims, 3 Drawing Figures Blood "doughnut" Target PuO micro spheres IO\ 3 34 5O Nickel source holder 22 minor axis 2\ v I i 38 34 l I n I n 5-|o mu Be wlndow Cryostat 5| Surface 200 mm Si(Li) Diode Detector PAIENTEI] JAN 2 21974 minor axis major radius B|ood "doughnu1 Turgei Pu0 micro spheres 200 r nm Si(Li) Diode Detector 3 34 5O I I7 Nickel source 38 holder 39 925: 40 22 53? ir 4| mmor axis 38 52 I2 I 4 49 Z\ y A N 2 3e 3418 3 n u v I 5-lO mil Be window Cryostat 5| Surface SOURCE HOLDER COLLIMATOR FOR ENCAPSULATING RADIOACTIVE MATERIAL AND COLLIMATING THE EMANATIONS FROM THE MATERIAL BACKGROUND OF THE INVENTION This invention was made in the course of, or under a contract with the United States Atomic Energy Commission.

During the past few years there has been a need for determining the levels of lead in biological samples, such as the blood of children in whom ingestion of paint flakes can represent a source of injurious lead levels. These are up to about 0.08 mg or more, where normal levels vary between 0.02 mg% to 0.04 mg% i.e. 0.2 parts per million (ppm), here 0.02 mg 5 0.2 mg Pb/ 100 g blood E 0.2 ug/ml 0.2 ppm. determining these lead levels, such as the well-known qualitative and/or quantitative laboratory chemical tests used for determining unknown contaminants in samples, but these systems have been expensive and time consuming, they have had an accuracy dependant on the skill of the person running the tests, and/or they have required extensive manipulation of the samples, such as by prior chemical separation of the contaminants from the sample.

SUMMARY OF THE INVENTION This invention overcomes the above-mentioned problems by providing, in one embodiment, an annular X-ray fluorescence system using a molded, doughnutshaped, sample configuration around a low energy radioactive source that is shielded from an X-ray detector in close proximity to the sample. With the proper selection of components, as described in more detail hereinafter, the desired detection is achieved.

Briefly stated, in one embodiment, this invention provides 360 irradiation of a molded, doughnut-shaped sample around an annular array of low energy radioactive material that is encapsulated and shielded from an X-ray detector by a collimator that collimates the primary emissions from the radioactive material away from the detector and toward the sample, the latter being in a plane that passes through the annular array and the molded, doughnut-shaped sample. Thedetector provides the desired X-ray fluorescense analysis, I

since it is shielded from the primary emissions from the radioactive material but still efficiently receives the secondary X-ray emissions from the sample that are produced therein around 360 by the collirnated primary emissions from the annular array of radioactive material. One construction provides a radioactive source comprising an annular array of spheres of low energy encapsulated radioactive material for selectively exciting specific X-rays in the sample, and means having a semiconductor detector for detecting these X-rays for X-ray fluorescence analysis.

It is an object of this invention, therefore, to provide the detection of lead in blood by low energy X-ray fluorescence analysis in a doughnut-shaped sample irradiated around 360 in a quick, accurate and simple system, without prior separation of the lead from the sample.

The above and further novel features and objects of this invention will become apparent from the following description of one embodiment when read in connec- 2 tion with the appended drawing, and the novel features will be particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings where like elements are referenced alike:

FIG. 1 is a partial top view of the collimator of one embodiment of this invention;

FIG. la is a detail taken from FIG. 1;

FIG. 2 is a partial cross-section of the apparatus of FIG. l through II II;

DESCRIPTION OF PREFERRED EMBODIMENT This invention provides a transportable device capable of detecting low levels of metal contaminants in biological samples with a minimum of sample preparation. In one embodiment, this invention detects normal levels of lead in blood, e.g., up to 0.02 mg%, and as such this invention provides a method and apparatus adapted for field use for screening blood samples for lead. However, higher levels of lead than 0.02 mg% can be detected in blood or other samples in accordance with this invention for research purposes, or on an au tomatic basis, as will be understood in more detail from the following. It will be understood by one skilled in the art that the system of this invention can and has also been used to detect trace elements in any sampleniolded into a doughnut, such as water, air pollution filters, etc.

In understanding this invention, it is known that fluorescence can be used for detecting elements in a sample. Simply stated,the X-ray fluorescence method of analysis consists of the detection and measurement of the characteristic X-rays given off by the atoms of the elements in the sample on production of excited states, the excited states of the atoms referring to the creation of vacancies in the normally occupied electronic energy levels, e.g., the M, L, or K energy levels. In this regard, after vacancies have been created, the subsequent readjustment of the electrons leads to the emission of specific X-rays with well-known energies that are characteristic of the elements, the energy required to produce the vacancies being known and the vacancies having been created by calibrated energy sources of irradiation, such as electrons, protons, alpha parti-v cles, or photons of sufficient energy to remove an electron from one of the electron shells of the atoms. Since the electronic energy levels of -all the elements of the sample are discrete, and there is a finite difference in these levels between the elements thereof, accurate measurement of the energies emitted during the excitation of the sample has made it possible to identify many of the elements in a variety of samples.

Of the two systems known heretofore for X-ray fluorescence analysis, the energy dispersion method has certain advantages over the wavelength dispersion method, the former being employed in accordance with this invention to achieve a portable detector system. To this end, it is known that the energy dispersion method has a high efficiency by eliminating the use of diffraction crystals and collimators used heretofore in connection with the wavelength dispersion method and by bringing a detector whose output is a function of the energy deposited therein close to the sample being analyzed. By using this method with such a detector, the

entire spectrum of the X-rays produced in the sample may be measured by electronic sorting of the detector pulses.

Applications of the desired energy dispersive method, such as in industrial applications for the multielement analysis of samples containing elements down to sodium in the periodic chart, are described in the New York University Institute of Environmental Medicine Report NYU-3040, by Laurer, the inventor herein, and Kniep, Wrenn, and Eisenbud. This invention utilizes this above-mentioned energy dispersive X-ray fluorescence method for detecting lead in blood, by employing a doughnut-shaped blood sample that is irradiated around 360 by collimated primary emissions passing through a collimator from an annular array of encapsulated radioactive source material at the center of the doughnut-shaped sample, the sample encircling the collimator for shielding the detector from the primary emissions from the source material. As will be understood in more detail hereinafter, one embodiment of this invention employs a specific arrangement having a detector, such as the semi-conductor detector that has recently been developed, the detector outputs being a function of the energy of the secondary X-ray emissions from the sample that are produced therein by the primary emissions from the source. This invention utilizes, in one embodiment, a specific radioactive source in a compact arrangement for providing a portable device for detecting lead in a blood sample both quantitatively and qualitatively without prior separation of the lead from the blood.

Referring to the drawings, the apparatus of this invention, in a preferred embodiment, consists of a source holder separated from a detector 24 which receives and measures emitted secondary X-rays, as will be described later.

Holder 10 consists of a disc-shaped collimator 17 formed from a pair of trapezoidal shaped metal collimating means 34 and 34' assembled with slanted sides 38 and common bases 36 as shown, to form an annular collimating rectangular shaped channel 42 in its edge 39, and a smaller inner annular channel 40 concentric with channel 42. Channel 40 is filled with source material 12 in an annular array 14, as described later. Edge 39, as described below, supports the blood sample 22 along a minor axis 41, in a sample holder doughnut 52 to be irradiated. One suitable material for doughnut 52,

is millipore absorbent pad made from white cellulose material that forms a blotter. In practice, it has been found, that no extraneous interfering fluorescence peaks are produced by the blotting material of the retaining blood container doughnut 52. The latter is supported by collimator 17 by a press fit on outer edge 39.

From the configuration illustrated, it is seen that the sample 22 can be very close to the source of the radiation without interfering with the collimation effected by means 34 and 34. Collimator 17 would be made from suitably material, such as nickel, which will provide proper shielding against the radiation from source material 12.

Located within rectangular channel 42 is an annular shaped beryllium exit window 50 between the radioactive source material 12 located within channel 40 and sample holder doughnut 52, in order to retain the radioactive source material withinchannel 40 and also to transmit as a filter the desired primary radiation from the source material to the blood sample.

Detector 24 is located within a cryostat 51 cooled by liquid nitrogen in order to produce an output 26, and to retain the resolution capabilities of the detector ma terial to be described below and as is understood in the art. Output 26 would be employed as is understood in the art and as described below to produce a spectral analysis from which the presence of lead can be detected and measured.

Collimator 17 is situated directly on cryostat 51 adjacent to or in contact with a beryllium window 49 permitting the X-rays emitted from the samle within container 52 to pass as shown by the arrows unimpeded in the direction ofdetector 24. It will be noted that the annular source holding channel 40, annular beryllium window 50, and annular sample holding container 52 centered on axis of rotation 23, are all situated in a common plane that is parallel to window 49 in cryostat 51 so that detector 24 is effectively equidistant from all of the above elements of the arrangement.

A suitable radioactive source material 12, which forms an annular centered core means for use in channel 14, comprises an annular array of micro-spheres of about 250p. diam. made from PuO Pu decays by alpha particle emission with a half-life of 86 years so that replenishment of this material during the normal life time of the apparatus is not required. The uranium- 234 daughter of this isotope emits L X-rays of 11.6 KeV, 13.5 KeV, 17.0 KeV and 20.2 KeV in approximately 13 percent of its disintegration. These X-rays are close to the L absorption edge of lead, resulting in a substantial increase in the absorption by lead of the X-rays. The effect of the radiation from the luO source material is to cause the lead present in the samplc to emit secondary X-rays which can be detected and measured by detector 24.

In operation, a blood sample to be tested for lead is drawn by capillary action into a hematocrit tube and then droppered one drop at a time for the retention and molding thereof into an absorbent material pre-cut in the form of the described blood container doughnut 52. The latter is then inserted on collimator 17, as shown in the drawing. Radiation from source 12 is collimated For purposes of calibration, a standard lead solution can be added to a sample of lead-free whole blood from which an aliquot can be drawn and spun to separate the red blood cells containing percent of the blood lead burden. Spinning e.g. in a centrifuge, effectively concentrates the lead in the sample'by a factor of about two. After spinning by centrifuging, the portion con-' taining the red blood cells can be dropped onto the container formed by doughnut 52, the detector being calibrated by standard methods using a standard radioactive source and a single channel analyzer.

The following is an example of this invention:

EXAMPLES A blood sample was used for the detection only of the lead X-rays therefrom, unlike other fluorescence analysis directed at the detection of X-rays of several ele-.

ments simultaneously, and the choice of materials and their annular doughnut-shaped arrangement, in accordance with this invention, ensured irradiation of the sample doughnut around 360 in the plane of the source, even when bringing the source to within 1 mm of the surface of the sample, and the sample to within 1 mm of the detector entrance window. Also, fluorescent X-rays did not substantially contribute to the lead X-ray energy region, since the doughnut-shaped arrangement of this invention minimized scattering from the source structure, while maximizing the sample fluorescence to scatter ratio. in this regard, without the described arrangement one of the significant contributions to background counts in energy dispersion fluorescence analysis was found to be due to scatter, both coherent and incoherent, of the primary excitation X- rays off the structural materials and the sample itself.

A semiconductor X-ray detector having high resolution and intrinsic efficiency was used. One detector used was a lithium drifted, silicon [SI(Li)] detector. This type of detector, as described in US. Pat. Nos. 3,381,367 and 3,278,668 has a silicon intrinsic region and a lithium drifted region, as is well known in the art in connection with these and standard Ge detectors, which can alternately be used, the latter being described in Brookhaven Nat. Lab. Report-BNL 16610. Below about 16 kc V the 3 mm thick Si(Li) detector used had about 100 percent efficiency, and the L-shell X-rays of lead detected were all below this energy, lead X-rays having, e.g., energies of 14,762 ke V (L y 12.620 ke V(L 12.611 ke V (L 10.549 ke V(L ),or1 48 ke V(L The detector was housed in a vacuum tight container having an X-ray entrance window, comprising a 5 mil thick beryllium window 49, which was selected for 100 percent transmission of the secondary characteristic X-rays from the blood sample above kc V. In order to retain superior resolution capabilities, the Si( Li) detector was cooled to liquid nitrogen temperatures.

A calibration curve for the Si(Li) detector used was made with a C0 source with photon energies of 6.399 ke V, 7.057 ke V and 14.40 ke V. This provided an energy calibration wherein the midpoint of the 10.5 keV Pb L X-ray peak appeared in channel 270 of the analyzer.

The following instruments were employed with a 200 mm Si( Li) detector 24:

1. Preamplifier:

2. Spectroscopy Amplifier:

A blank sample doughnut provided a first multichannel analyzer output, yielding a lead-free background count. Thus changing doughnuts containing lead produced the qualitative and quanitative channel output characteristic of the lead present in the doughnut.

Selection of the detector size was based on the two factors of resolution and geometrical efficiency. To this end, the resolution was good enough to separate one, if not both, of the most abundant L X-rays from the lead in the blood sample, i.e. 10.5 ke V and 12.6 ke V, from the other X-rays from the blood sample. The detector area was as large as possible to obtain maximum geometrical efficiency.

Since the resolution obtainable from the Si(Li) detector was an inverse function of its size, the size chosen was a compromise dictated primarily by the other X-rays from the blood. Table 1 lists the normal values with ranges of the electrolyte content of human blood as follows:

While there were a great number of elements in the blood sample, all of which could contribute more or less to matrix effects in the sample, rubidium 300 ,ug/lOO ml), bromine 800 rig/ ml) and zinc 900 ,u.g/100 ml) were the elements requiring the most careful consideration in terms of their possible spectral interference with the lead peaks in the output signals produced by the detector.

It was found in practice that the K a and K of bromine, at 11.9 ke V and 13.4 ke V, and the 15.1 ke V and 13.35 ke V K and K, peaks of rubidium bracketed the 14.7 ke V L and 12.6 ke V L X-rays of the lead in the blood sample, while the bromine (1 1.9 ke V) and the 9.6 ke V K B X-rays of zinc bracketed the 10.5 ke V L X-rays of the lead. However, due to its low abundance and its close proximity to the K X-rays of rubidium, the L y X-ra'ys of the lead were avoided, and instead, the detector analyzed the remaining K (10.5 ke V) and L (12.6 ke V) X-rays of the lead, both of which were separated by about 900 ev from the possible interfering X-rays. Thus, the minimum resolution was about 350 ev, f w h m (full width of peak at l maximum height). To this end, a 200 mm Si(Li) detector width guaranteed resolutions of 300 ev,fw h m, at the 5.9 ke V Mn K energy was used. The actual system used had a guaranteed resolution of 270 ev, f w h m (5.9 ke V), which was checked using 6.4 ke V Fe K X-ray s, at 280 ev,fw h m. A system actually used was an ortec Model. No. 7016-16270, from Oak Ridge, Tenn.

Due to satisfy considerations for the portable device of this example, the source was generally kept to milli curie strengths, which, how'ever,1imited the available primary output emissions therefrom to the order of 10 to 10 photons/sec. To obtain an isotopic source having the correct emissions for the required efficient excitation of the sample, equal size Pu microspheres'of Pu0 having diameters of 250p. were desirable although larger or smaller diameter sources could be used. This sphere size has an activity per sphere as shown from the following Table II:

TABLE II Volume 4/3 11' r 4.2 (1.25 X 10 cm) '=8.15X10 cm v 1 Mass of Pu 8.15 X 10*'cm X 7.35 gm/cm 6.0 X 10 gm Pu Pu activity 6.0 X gm X 17.5 Ci/gm 105 X 10- Ci or z 1.0 mCi/250 p. sphere PuO This gives 25 m Ci of activity in a 2 mm diameter circle forming the minor axis of the annular array of radioactive microspheres, i.e., the encapsulated pellets.

The sources was advantageously free of interferring radiations, and had a reasonable cost. In this regard, a plutonium-238 source decays by alpha particle emission with a half-life of 86 years, while the uranium-234 daughter emits L X-rays of 11.6 ke V, 13.5 ke V, 17.0 ke V and 20.2 ke V in approximately 13 percent of its disintigrations. In this regard, the uranium L X-rays are 2.5 times greater than those of "Cd.

One source, which was actually used, was a 4 mm diameter m Ci source from Amersham-Searle, which utilized five 1 mm diameter bead-shaped pellets, each containing 4 m Ci Pu for a total activity of 20 mi Ci sandwiched by 0.5 mm Cu discs, while awaiting the desired source from mound Laboratories. In regard to the latter Pu spheres in the form of PuO from 50;; to 400p. in diameter, the 250p. spheres desired have an activity per sphere calculated as indicated above. Thus arranging microspheres, as shown in the drawings, it is possible to obtain m Ci of activity in a 2 mm diameter circle.

To obtain the lowest possible detection limit with the described X-ray flux, the design of the annular source, holder and collimator of this invention optimized the source-sample-detector geometry by placing the sample close to the detector to maximize detection efficiency, while minimizing the number of directly transmitted X-rays from the source to the detector, minimizing the scatter and fluorescence from the structural materials around the source, and maximizing the fluorescence to scatter ratio from the sample. Moreover, the annular doughnut-shaped design of the source sample geometry, in accordance with this invention, provided for the majority of excitation photons to scatter at the best angles for increasing the energy increment between the lead Xrays and the scatter interference, and reducing the number of scattered photons.

To this end the blood sample was molded into a ringshaped doughnut for forming a doughnut-shaped target that was irradiated around 360. The doughnuts were cut with an 8 mm outer diameter and a 4.2 mm inner diameter to allow the sample to slip easily over the 4 mm source. Crosshairs, which held the source in position, also kept the doughnut in position around a beryllium exit window 50 for the source in the collimating space formed in the collimator.

During preparation, the doughnut was held on a 4.2 mm diameter shaft with a base fixture cut from a polytetra-fluoroethylene rod to which the blood did not adhere. A filter-paper-like toroidal blotter 0.8 mm thick was shaped to form the doughnut, and after the addition of the blood sample thereto the doughnut was placed under a heat lamp to dry while still on the shaft. Adequate drying was accomplished in 3 to 4 minutes, after which the doughnut was ready for fluorescence analysis by placing the doughnut around an annular array of encapsulated radioactive pellets built as a hollow central core close to the sample around 360, while the sample, which was shieldedform the source by the collimator, was close to the detector around 360. This configuration allowed irradiation of the sample throughout the 360 in the'plane of the source, while the source was brought to within a distance of about 1 mm from the surface of the sample, and the sample was brought to about 1 mm from the Be entrance window 49 of the detector cryostat 51. The detector position within the cryostat was fixed by the manufacturer at a minimum distance of 5 mm from the window entrance of a vacuum tight container cryostat 51.

In the doughnut-shaped configuration of this example, a 1 mm collimation space between the source and the sample prevented direct transmission of the source emissions from the source to the detector, and by placing the source inside the sample, external structural material was eliminated, thus limiting scattering interference to the sample itself, while a minimal amount of scattering and fluorescence from the edges of the source holder formed by the collimator was produced thereby. Moreover, the collimator was constructed of nickel so that its fluorescence X-rays did not interfere with the 10.5 ke V Pb region. Still further, because of the direction of the source emissions caused by the de scribed configuration and collimatorwith respect to the detector, the scattering was predominantly thus taking advantage of the reduction in the number of photons scattered at that angle in the energy region of interest, and the increased energy separation between the 90 scatter and the Pb fluorescence energies.

It was found that this configuration thus minimized the background due to scattering and fluorescence of external structural materials, while increasing the analyzer output signal through the closest possible proximity of both the source-sample and the sample-detector. Estimates of the geometrical efficiency for the configuration used in this example were approximately 1 l percent for the source to the sample and 10 percent for the sample to the detector with a 8 mm diameter Be entrance window 49 on the cryostat, as shown in the drawings. Due to the symmetry of the source and sample, the sample-detector efficiency may be increased to 20 percent by the proper use of two of the described detectors.

The system sensitivity and detection limit for the measurement of lead in blood using the described 20 m Ci, Amersham-Searle source were determined by adding known amounts of a standardized lead solution 'to measured amounts of normal blood. The standard lead solution used contained 1,000 ppm or 1 mg Pb/ml. One tenth m1 of standard, i.e., pg Ph, was added to 10 ml of blood to make a solution containing 100 pig/10.1 ml 9.9 ng/ml 9.9 ppm. Nine blood solu tions were made up containing 0.5, 1.0, 2.0, 3.3, 4.3, 5.0, 6.2, 7.4, and 9.9 ppm of lead. e

Blood samples for count rate determinations'were made up in doughnuts using aliquots of 75 pl from each of the nine solutions, which were dropped into the doughnut and dried.

Ten l-minute counts were run for each of the samples, from which the mean standard deviations was calculated as representative of the count rate from that sample. The average count rate of a 75 1.1.1 aliquot of normal blood with no lead added, also counted 10 times, was then subtracted from the nine samples. The resultant curve was compound as a straight line (p. 0.994), with a slope of.29.7 cpm/ppm.

The following Table III, summarizes the results of the above:

While the above has described a portable device capable of detecting normal levels of lead in blood with a minimum of sample preparation in a short analyzing time, it will be understood that this device can be used for screening in field use, as a research device, and/or in an automated system. To this end, in terms of basic parameters, i.e., background sensitivity, detection limits, and drift (base line and gain) each of these systems will be identical while the instrumentation will be different. in this regard, aside from the power supply, the screening system which provides a yes-no decision, will operate with only an amplifier,- single-channel analyzer, and sealer-timer readout. On the other hand, the research system, which is used for quantitative measurements, is equipped to monitor the entire energy range from about 2 ke V kc V. The latter requires an additional multi-channel analyzer. For automatic operation, an automatic print-out and point plotter for spectrum observation and analysis are added. In the case of automatic operation with the screening system, overnight runs would require the addition of an automatic printer scaler.

What is claimed is:

1. Apparatus for encapsulating radioactive material and collimating the emanation therefrom for the detection by the principles of X-ray fluorescence analysis of a metal contaminant in a sample, comprising:

a. material forming a radioactive source of emissions;

emissions with the sample about 360 to produce secondary emissions that are received by said detector, said secondary emissions being characteristic of said metal contaminant in the sample, said secondary emissions being detected by said detector as a measure of said metal contaminant in said target sample for energy dispersion analysis in accordance with the principles of X-ray fluorescence analysis.

2. Apparatus for encapsulating radioactive material and collimating the emissions therefrom for the detection by X-ray fluorescence of a metal contaminant in a biological sample, comprising:

a. centered, core, first means forming an annular array of radioactive material in a plane for producing primary emissions from said radioactive material;

b. disc-shaped second means forming a holder with a groove around its outside edge for holding, enclosing and containing said annular array of radioactive material and for collimating said primary emissions therefrom outwardly in said groove in a direction away from the center of said annular array in the plane of said annular array;

. doughnut-shaped third means forming an annular ring-shaped container for molding said biological sample into a corresponding shape, said container being centered on the axis of rotation of said annular array around the groove formed by the second means and around the centered, core, first means in the plane of the annular array thereof for receiving the collimated emissions from said radioactive material for interacting the same width said biological sample in said doughnut-shaped third means for producing characteristic secondary emissions from said metal element that contaminates said biological sample; and

d. fourth means forminga detector adjacent said doughnut-shaped third means that is shielded from said radioactive material arid said emissions therefrom by said disc-shaped second means for detecting and analyzing said characteristic secondary emissions from said biological sample in said container by X-ray fluorescence analysis.

3. The apparatus of claim 2 in which said characteristic secondary emissions are X-rays given off by the atoms of said metal element due to the production of excited states therein by said primary emissions, said fourth means providing an X-ray fluorescence detector for said X-rays given off by said metal element.

4. The apparatus of claim 2 in which said characteristic secondary emissions areX-rays given off by the atoms of said metal element due to the production of excited states therein by said primary emissions incident thereon in said biological sample in said third means, and said fourth means distinguishes said characteristic secondary emissions by energy dispersion as a measure of the amount of said element present'in saidbiological sample, whereby said fourth means produces an output as a function of the energy deposited therein by said characteristic secondary emissions.

5. The apparatus of claim 2 in which said fourth means has a semi-conductor selected from the group consisting of silicon, germanium, and lithium drifted semi-conductor detectors, and means for producing therefrom an output proportional to the energy of the characteristic secondary emissions received by said detectors from said biological sample as a nondestructive, portable, qualitative, and quantitative measure of the amount of said element that contaminates said biological sample without prior chemical separation from said sample.

6. The apparatus of claim 2 in which lead is the metal element that contaminates said biological sample, which is blood, and said fourth means is responsive to the characteristic secondary emissions from said lead for producing an output proportional to the amount of said lead in said biological sample.

7. The apparatus of claim 2 in which said fourth means is responsive to characteristic secondary emissions, consisting of 10.5 and 12.6 ke V K producing an output proportional to the amount of lead that contaminates said biological sample.

X-rays for I 8. The apparatus of claim 2 in which said fourth means has a vacuum tight container that is cryogenically cooled, and a beryllium window for said fourth means, said latter means selecting and detecting the secondary emissions characteristic of a lead contaminate in a biological sample' of whole blood in said doughnut-sahped third means.

9. The apparatus of claim 2 in which said first means is Pu for producing primary emissions in the energy range of the L absorption edge of lead and characteristic secondary emissions in the range of to 10 photons/second for the detection by said fourth means.

10. Apparatus for the detection of a metal contaminant in a sample by the measurement of secondary radiation emission from the contaminent induced by radioisotopic excitation comprising:

a. means for encapsulating and shielding against radiation emanations an annular array of a radioisoto- 

2. Apparatus for encapsulating radioactive material and collimating the emissions therefrom for the detection by X-ray fluorescence of a metal contaminant in a biological sample, comprising: a. centered, core, first means forming an annular array of radioactive material in a plane for producing primary emissions from said radioactive material; b. disc-shaped second means forming a holder with a groove around its outside edge for holding, enclosing and containing said annular array of radioactive material and for collimating said primary emissions therefrom outwardly in said groove in a direction away from the center of said annular array in the plane of said annular array; c. doughnut-shaped third means forming an annular ring-shaped container for molding said biological sample into a corresponding shape, said container being centered on the axis of rotation of said annular array around the groove formed by the second means and around the centered, core, first means in the plane of the annular array thereof for receiving the collimated emissions from said radioactive material for interacting the same width said biological sample in said doughnut-shaped third means for producing characteristic secondary emissions from said metal element that contaminates said biological sample; and d. fourth means forming a detector adjacent said doughnut-shaped third means that is shielded from said radioactive material and said emissions therefrom by said disc-shaped second means for detecting and analyzing said characteristic secondary emissions from said biological sample in said container by X-ray fluorescence analysis.
 3. The apparatus of claim 2 in which said characteristic secondary emissions are X-rays given off by the atoms of said metal element due to the production of excited states therein by said primary emissions, said fourth means providing an X-ray fluorescence detector for said X-rays given off by said metal element.
 4. The apparatus of claim 2 in which said characteristic secondary emissions are X-rays given off by the atoms of said metal element due to the production of excited states therein by said primary emissions incident thereon in said biological sample in said third means, and said fourth means distinguishes said characteristic secondary emissions by energy dispersion as a measure of the amount of said element present in said biological sample, whereby said fourth means produces an output as a function of the energy deposited therein by said characteristic secondary emissions.
 5. The apparatus of claim 2 in which said fourth means has a semi-conductor selected from the group consisting of silicon, germanium, and lithium drifted semi-conductor detectors, and means for producing therefrom an output proportional to the energy of the characteristic secondary emissions received by said detectors from said biological sample as a non-destructive, portable, qualitative, and quantitative measure of the amount of said element that contaminates said biological sample without prior chemical separation from said sample.
 6. The apparatus of claim 2 in which lead is the metal element that contaminates said biological sample, which is blood, and said fourth means is responsive to the characteristic secondary emissions from said lead for producing an output proportional to the amount of said lead in said biological sample.
 7. The apparatus of claim 2 in which said fourth means is responsive to characteristic secondary emissions, consisting of 10.5 and 12.6 ke V K X-rays for producing an output proportional to the amount of lead that contaminates said biological sample.
 8. The apparatus of claim 2 in which said fourth means has a vacuum tight container that is cryogenically cooled, and a beryllium window for said fourth means, said latter means selecting and detecting the secondary emissions characteristic of a leaD contaminate in a biological sample of whole blood in said doughnut-sahped third means.
 9. The apparatus of claim 2 in which said first means is 238Pu for producing primary emissions in the energy range of the L absorption edge of lead and characteristic secondary emissions in the range of 107 to 108 photons/second for the detection by said fourth means.
 10. Apparatus for the detection of a metal contaminant in a sample by the measurement of secondary radiation emission from the contaminent induced by radioisotopic excitation comprising: a. means for encapsulating and shielding against radiation emanations an annular array of a radioisotopic excitation source material emitting radiation capable of exciting said contaminant to produce secondary radiation emission; b. means for carrying said sample in a plane common to said array concentric to, spaced from, adjacent to and surrounding said array; c. said encapsulating means including means to collimate radiation emanation from said array along said plane to said sample carrying means to cause secondary radiation emission from said contaminant within said sample; and d. detection means spaced from, and shielded from said array by said encapsulating means to detect and measure the secondary emissions from said sample. 